JPH0474825A - Method for controlling temperature of steel sheet in continuous heating furnace - Google Patents

Abstract

PURPOSE:To suppress the deviation of the temp. of a steel sheet as far as possible and to execute sure temp. control by calculating the pass speed to compensate the 'amt. of deviation from a target value' from the predicted deviation of the sheet temp. at the outlet of a heating furnace and continuously changing the pass speed by presetting. CONSTITUTION:A strip 1 formed by welding plural coils of different kinds is passed in a white arrow direction in the continuous heating furnace 2. The specifications and position information of the coils are sent to a sheet temp. controller (model I) 6 at this time. The set value of the furnace temp. and the timing for changing this value, the set value of the pass speed and the timing for changing this value are set and the optimum transition orbit of the sheet temp. is predicted. The flow rate of fuel flowing into radiant tubes 8 is controlled in accordance with this information in the furnace temp. controller 7. Further, the width of the deviation from the target sheet temp. is calculated from the 'predicted transition orbit of the sheet temp.' and the set value of the pass speed is determined in an additional sheet temp. controller (model II) 9. A driving roll 3 is so controlled that the pass speed attains the above- mentioned set value via a speed controller 10.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is applicable to welding various steel plates having different "plate thickness", "plate width", "material", or "target temperature at the outlet of a heating furnace", for example. The present invention relates to a "temperature control method for steel plates" when the steel plates are continuously passed through a heating furnace for heat treatment.

<Prior art and its issues> In general, cold-rolled prepared plates are subjected to various heat treatments that combine heating, soaking, cooling, etc. in order to impart the desired properties. From a sexual perspective, it is usually done continuously and at high speed.

However, in recent years, steel plates processed in continuous heat treatment furnaces (continuous annealing furnaces) have been welded with coils of different plate thicknesses, plate widths, materials, etc., reflecting the increasing demand for a wide variety of products and small lots. - The number of cases where the heat treatment furnace continues is rapidly increasing, and it is therefore necessary to frequently change the furnace temperature setting of the heat treatment furnace.

By the way, as a heating method in a heating furnace, an indirect heating method using a radiant tube, etc. is widely adopted from the viewpoint of preventing oxidation of the steel plate, but this method has a proven track record when changing the furnace temperature setting. The drawback is that the followability of the furnace temperature value is extremely low.

For example, as exemplified by the operation of a heating device proposed in JP-A No. 57-35640, in continuous heat treatment of steel plates after welding and joining different steel plates, the welding point of the steel plate entering the heating furnace is It is necessary to control the steel plate temperature before and after reaching the boundary, but in this case, the "amount of change in the furnace temperature setting" and the "timing of displacement" should be calculated in advance according to various operating conditions, and then the temperature should be controlled. The furnace temperature setting value is changed based on the calculation result.

Figure 1 shows an example of controlling the temperature of a steel plate using the above device, and explains the control method in a welded section of ``steel plates that have the same width, material, and target temperature, but differ only in thickness.'' However, as shown in Fig. 1, the set value of the furnace temperature should correspond to the change in plate thickness (the state shown by the broken line).

However, the actual value of the furnace temperature follows a change course as shown by the solid line due to poor followability. Therefore, the steel plate temperature will deviate from the range shown by hunting before and after the welding point with respect to the target temperature.

If the steel sheet temperature deviates from the target temperature in this way, the steel sheet will be "under-baked" or "over-baked" and the yield as a product will be reduced.

Therefore, in order to eliminate such "deviation from the target temperature", a method that uses "control to change the steel plate threading speed" in addition to the above-mentioned "change of the furnace temperature setting" is proposed in JP-A-61. -1
It was proposed as No. 90026. In this method,
In addition to providing a plate temperature control model that dynamically expresses the relationship between the steel plate temperature at the outlet of the heating furnace (hereinafter simply referred to as "plate temperature"), furnace temperature, fuel flow rate, plate thickness, plate width, and strip threading speed, When changing the plate thickness, plate width, or target plate temperature value in the future (hereinafter referred to as "set change"), use this model to determine the "optimum transition trajectory of plate temperature," the "optimum amount of change in plate threading speed," and " Calculates the optimal timing to start changing speed and based on the results “
"Control that includes changing the threading speed only once discontinuously"
The key point is to implement the following.

However, even with the method proposed in JP-A-61-190026, the plate thickness at the time of cent.
To completely eliminate the problem that when the amount of change in the plate width or target plate temperature value is large, the plate temperature deviates from the target value over a relatively long period even if the optimum transition trajectory of plate temperature is achieved. I couldn't.

In other words, as shown in the sand pattern area in Figure 2, each steel plate has a tolerance range for the plate temperature to be off target, which is determined by its grade, etc. (hereinafter, the tolerance range for the plate temperature to be off target is simply referred to as
In the method disclosed in JP-A No. 61-190026, there is also a "plate temperature deviation (deviation of the plate temperature from the permissible range)" shown by hatching in FIG. 2 before and after the set change.
There was still concern that the copper plate would be overcooked or undercooked.

For this reason, the purpose of the present invention is to accurately deal with this even when it is expected that the optimum transition trajectory of the plate temperature at the time of set change will cause the plate temperature to deviate. The objective was to establish a ``plate temperature control method in a continuous heating furnace'' that could effectively avoid overheating.

Means for Solving the Problems> As a result of intensive research to achieve the above object, the inventors were able to obtain the following knowledge. That is, different types of steel plates with different (al) plate thicknesses, plate widths, or target plate temperatures at the outlet of the heating furnace are welded to form continuous steel plates, which are continuously fed into the heating furnace. When heat-treating the plate by passing it through the plate, first, the plate temperature and heating furnace temperature (plate temperature and heating furnace temperature ( Hereinafter, the plate temperature control model (hereinafter simply referred to as “furnace temperature”) is shown in Fig. 3, which represents the dynamic relationship j with
Namely, plate temperature and furnace temperature.

If you use the plate temperature control model (hereinafter referred to as "Model I") that dynamically expresses the relationship between plate thickness, plate width, and threading speed,
When changing cents in the future, the optimal transition trajectory for plate temperature (at this stage, only one discontinuous speed change is considered, so this "optimum transition trajectory" is defined as one discontinuous speed change) J, which is the optimal trajectory when
It is also possible to predict the amount of change in plate temperature at the outlet of the heating furnace.

(b) From the above “deviation amount of plate temperature from the target value” and some other data obtained from model
It is possible to predict the ``optimum threading speed before and after the welding point of the steel plate'' that can accurately compensate for the deviation of the plate temperature from the target value (C1). Create a sheet temperature control model (hereinafter referred to as "model ■") that compensates by If this is achieved, excellent temperature control with extremely small plate temperature deviations will be possible.

The present invention has been made based on the above-mentioned findings, etc., and is based on the following: [Predicting in advance the transition trajectory of the steel plate temperature up to the exit of the continuous heating furnace during continuous heating of "continuous steel plates" made by welding different types of steel plates. At the same time, in the plate temperature control method that compensates for the predicted temperature of the steel plate at the outlet of the heating furnace by pre-cent control using the furnace temperature and strip threading speed as manipulated variables when the predicted steel plate temperature at the outlet of the heating furnace deviates from the target value, the predicted ``target value'' By calculating the threading speed to compensate for the amount of deviation from the temperature and continuously changing the threading speed using a preset setting in accordance with this calculated value, the temperature deviation of the steel plate in a continuous heating furnace is minimized. It is characterized by the fact that it allows accurate temperature control to be carried out by

The method of the present invention can be applied to, for example, "a welding point detector that detects the welding point of a steel plate,""a speed detector that detects the threading speed of a steel plate,""a furnace temperature detector that detects the temperature of a heating furnace," and A "detector group" equipped with a "plate temperature detector that detects the temperature of the steel plate at the exit of the heating furnace" and a "detector group" that tracks the welding point of the steel plate according to the output signals from the welding point detector and speed detector.
A well-known sheet temperature control model (Model I) J that calculates the optimal transition trajectory of sheet temperature, the amount of change in sheet threading speed, and the timing of speed change when changing sheets in the future.
The plate temperature control model (Model II) J predicts deviation of the plate temperature from the target from the plate temperature trajectory and continuously changes the plate threading speed to compensate for this, and the plate temperature control model (Model II) J calculates the plate threading speed to the value calculated by the above model. The procedure is as follows.

That is, in the plate temperature control method according to the present invention, first, the model
The change trajectory of sheet temperature, amount of change in sheet threading speed, and change timing are determined by: Note that, as described above, the sheet temperature transition trajectory determined by Model I has been optimized on the assumption that the sheet threading speed is discontinuously changed only once during setting.

As is clear from FIG. 3, when the sheet temperature deviates upward from the target deviation tolerance range, the sheet threading speed is
(If you do this, the time the steel plate stays in the heating furnace will be shortened, and the plate temperature can be lowered.) On the other hand, if the plate temperature deviates downward, the plate temperature will be lower than the set value. By setting the speed, it is possible to reduce the area where the plate temperature deviates.

In addition, model ■ calculates the "threading speed that compensates for the amount of deviation from the target sheet temperature" using the following calculation method based on the "amount of deviation from the target sheet temperature" calculated from the trajectory of the sheet temperature predicted by model I. This is to calculate and continuously control the sheet threading speed with a preset setting. When this is added, the control state shown in FIG. 3, for example, is improved as shown in FIG. 4.

Step I Using the model, the trajectory of the change in plate temperature, the amount of change in the threading speed, and the timing of the change in the speed are determined.

At this time, as shown in FIG. 3 above, hl: thickness of the preceding material, h2: thickness of the succeeding material.

tI: Furnace temperature set value change time.

t2: Time when the furnace temperature reaches a steady state.

t3: Speed change timing.

t4: Time at which the plate thickness changes at the outlet of the heating furnace.

TFI: Furnace temperature set point in steady state of preceding material.

TF2: Furnace temperature setting value in a steady state of the succeeding material; : Threading speed in a steady state of the preceding material.

v2: Threading speed in steady state of trailing material.

ΔT: The width of deviation from the target plate temperature at the tail end of the preceding material.

ΔT2: Back 2: Width of deviation from target plate temperature at the tip.

(As for the plate temperature, if it deviates upward from the target plate temperature, ΔT>0. If it deviates downward, ΔT<0,
The plate widths of the preceding material and the succeeding material are the same and are defined as W).

■　Step■ Preceding material in a steel plate that is continued by welding.

Influence coefficients ε1 and ε2 defined below are calculated for each trailing material.

a) Definition of the influence coefficient ε of the preceding material The preceding material is speeded into the heating furnace at the furnace temperature T Assuming that in this steady state, if the strip threading speed is changed by Δ (actually, a Δ spread of 3 to 5χ is good), the strip temperature will change as shown in Figure 5. When the range of change in plate temperature due to
and have different signs, so ε, <0).

b) Defining the influence coefficient 62 of the succeeding material The influence coefficient 82 of the succeeding material is defined using the same procedure as for the preceding material.

■Step■ As shown in FIG. 6, the sheet passing speed calculated in step I is corrected in the following procedure.

i) Time t is t≦1. At the time point, the sheet threading speed V is set to .

ii) At the time t is 1=14-Δt, the sheet threading speed is set to t7=27. −β(ΔT,)/ε1.

Here, Δt refers to the following time.

That is, when changing cents, the threading speed may be changed discontinuously, but it is impossible to reduce the time required for this to zero due to the equipment, and this time is defined as Δt.

iii) When the time t is tl<t<t4-Δt, the sheet passing speed V is set to .

iv) When time t is 1=14, the threading speed is = v2-β(ΔT2)/ε2゜ Set to .

■) When time t is i4<t<tz, the threading speed V is Set to .

vi) When time t is tzt2, the plate threading speed is set to speed 2.

Note that it is also possible to change the threading speed in a curved manner instead of linearly, but due to the thermal inertia of the hearth rolls in the furnace, there is not much difference in the effect of the two, and therefore In consideration of the influence of the tension applied to the steel plate, etc., an example of the former method (method of linearly changing it) has been described here.

By the way, the path of the steel plate in the heating furnace has a finite length, and it is also affected by the thermal inertia of the hearth rolls in the heating furnace, so it is physically impossible to completely eliminate the deviation of the plate temperature from the target. It is noteworthy that by applying the sheet temperature control method of the present invention, sheet temperature deviation is significantly reduced and steel sheet quality is significantly improved.

Next, the present invention will be described in more detail based on explanatory drawings of examples.

<Example> FIG. 7 is a schematic diagram showing the configuration of a "temperature control device for a steel plate in a continuous heating furnace" according to the present invention.

A strip formed by welding a plurality of coils with different plate thicknesses, plate widths, target plate temperatures, or materials (11 is a continuous heating furnace (2)
The sheet is passed through by the drive roll (3) in the direction of the white arrow.

At this time, determine the coil plate thickness using the steel plate specification setting device (4).

The specifications of the plate width, emissivity, and target plate temperature, as well as the coil position information are sent from the tracking device (5) to the conventional plate temperature control device (Model I) (6). Then, in this conventional plate temperature control device (model I) (61), the set value of the furnace temperature and its change timing, the set value of the sheet threading speed and its change timing are determined, and the optimum transition trajectory of the plate temperature is predicted. The set value of the furnace temperature determined here and its change timing are sent to the furnace temperature control device (7), which controls the flow into the radiant tube (8) based on the information. control the fuel flow rate.

Here, the plate temperature transition trajectory predicted by the conventional plate temperature control device (Model I) (6) described above is as shown in Fig. 3 because the plate threading speed is only changed discontinuously. Temperature deviation occurs over a long period of time. Therefore, in the example of the present invention, an additional plate temperature control device (model It) (8) is provided, which calculates the target plate temperature deviation width from the "predicted plate temperature transition trajectory" and The set value of the sheet threading speed is determined by the sheet threading speed optimization calculation method.

Note that there is a permissible range for the threading speed due to equipment or operational constraints, but if the set value calculated above exceeds this permissible range, the set value may be set to the permissible upper limit (or the upper limit is safely set). (a value multiplied by a coefficient α=0.9 to 0.95).

The speed setting value determined by the model (9) is sent to the speed control device αω, and the speed control device α@ controls the drive roll (3) so that the sheet passing speed becomes the above setting value.

Now, with respect to the conventional plate temperature control state shown in FIG. 3,
When the plate temperature control method according to the present invention is applied, a control state as shown in FIG. 4 is obtained, and deviations in plate temperature are significantly reduced.

<Summary of Effects> As explained above, according to the present invention, the width of deviation from the target temperature that occurs over a long range before and after the welding point can be significantly reduced during continuous heat treatment of a strip made by welding dissimilar steel plates. This brings about extremely useful effects industrially, such as making it possible to produce steel plates of excellent quality at a high yield.

[Brief explanation of drawings]

FIGS. 1 to 3 are graphs showing the state of control of the steel plate temperature by conventional methods, respectively. FIG. 4 is a graph showing the concept of the method of the present invention and the control state of the steel plate temperature. FIG. 5 is a graph for explaining the definition of the influence coefficient. FIG. 6 is a graph showing the control state of the steel plate temperature according to the method of the present invention. FIG. 7 is a schematic diagram showing a configuration example of a temperature control device for a steel plate according to the present invention in a continuous heating furnace. In the drawings: 1...Strip, 2...Continuous heating furnace. 3... Drive roll, 4... Steel plate specification setting device. 5...Tracking device. 6... Conventional plate temperature control device (Model I). 7... Furnace temperature control device. 8...Radiant tube. 9...Additional plate temperature control device (model ■). 10... Speed control device.

Claims (1)

[Claims] When continuously heating a "continuous steel plate" made by welding different types of steel plates, the trajectory of the steel plate temperature up to the exit of the continuous heating furnace is predicted in advance, and if the predicted steel plate temperature at the exit of the heating furnace deviates from the target value. In the sheet temperature control method that compensates for this by preset control using the furnace temperature and sheet threading speed as manipulated variables, the sheet threading speed that compensates for it is calculated from the predicted "deviation amount from the target value" and this A method for controlling the temperature of a steel plate in a continuous heating furnace, characterized by continuously changing a preset threading speed in accordance with a calculated value.